Methane, carbon dioxide and nitrous oxide are the main gasses with greenhouse effect.
Methane (CH4) is a greenhouse gas whose atmospheric concentration has increased dramatically over the last century and, after carbon dioxide, is the largest potential contributor to the warming of the Earth. The increase in tropospheric methane level correlates closely with global expansion in the human population. Consequently, it is believed that approximately 70% of methane emissions are associated with human activities. Land filling of waste and agricultural practices generate and release methane to the atmosphere in amounts that will increase as the number of people in the world grows.
Ruminants, which include cattle, buffalo, sheep, and goats, have a large fore-stomach where methane-producing fermentation occurs. The rumen digestive tract is made up of four gastric compartments, the rumen, the reticulum, the abomasum and the omasum. The largest and most important of these is the rumen. The rumen functions as a fermentation compartment. It contains large populations of microorganisms including methane producing archaea, which break down the plant material. Said microorganisms are commonly referred to as methanogens. Archaea populations use the hydrogen and carbon dioxide, products of the anaerobic microbial fermentation, to generate energy for growth, producing methane as an end product. Finally, methane is expelled out from rumen through eructation.
The production of methane by cattle and sheep represents a carbon loss pathway that reduces productivity. If the energy that is lost through methane synthesis could be rechannelled though other biochemical pathways, commonly to propionate synthesis, rumen fermentation would become more efficient and it would be reflected in the animal's weight gain or milk production improvements. It would be cost effective to the producer as well as to provide an effective tool to reduce methane emissions to the atmosphere. Indeed, because the lifespan of methane in the atmosphere is 12 years (while those of carbon dioxide and nitrous oxide are 100 years and 120 years, respectively) reducing methane emissions would have more a more rapid effect on the environment.
Past studies with ruminant animals have shown that methane production is affected by diet. By increasing the ratio structural/non-structural (cellulosic/starchy) carbohydrates, methane emissions increase. Moreover, the addition of lipids sources to the diet reduces enteric methane emissions. Although parallel to methane reduction, high fat supplementation rates reduce rumen microbial fermentation, feed intake and fibre digestibility. A number of chemical feed additives such as antibiotics, (i.e ionophores) or defaunating agents have been introduced into ruminant nutrition to promote growth, improve feed utilisation and decrease methane production. However, concerns over the presence of chemical residues in animal products and the development of bacterial resistance to antibiotics have stimulated the search for safer natural alternatives that would be useful in organic livestock farming.
Plants or plant extracts containing essential oils, tannins, saponins, flavonoids and many other plant secondary metabolites have been shown to improve rumen metabolism targeting specific groups of rumen microbial populations. Patraa A. K. and Saxenab J (2010). Phytochemistry, 71(11-12):1198-222 describes the use of plant secondary metabolites to inhibit methanogenesis in the rumen. Document WO2005000035 refers to a procedure to enhance ruminal fermentation and, in particular, reduce methanogenesis, consisting of the administration of a soluble alfalfa extract obtained from fresh alfalfa.
There is thus a need for alternative ruminant feed compositions comprising compounds of natural origin and which are both effective in reducing methane production and safe for its use in livestock farming.